Volume control



y 5, 1941- J. MARSTEN 2,240,565

' VOLUME CONTROL Fild Jan. 7, 1937 2 Sheets-Sheet 1 INVENTOR fg se Marsfen ATTORNEYS y 1 I J. MARSTEN I 2,240,565

VOLUME CONTROL Filed Jail. '7, 1957 2 Sheets-Sheet 2 INVENTOR Jesse Marsten BY @1 4, L

ATTQRNEYS Patented May 6, 1941 UNITED STATES PATENT OFFICEVOLUME-CONTROL Jesse Marsten, Philadelphia, Pa, assignor toInternational Resistance Company, Philadelphia,

Pa., a corporation of Delaware Application January '1, 1937, Serial No.119,469

6 Claims. (CL 201-55) I This invention relates to rheostats orpotentiometers, and more particularly to rheostats or potentiometers forvolume control in connection with radios.

One of the objects of this invention is to provide a rheostat orpotentiometer which is simple in construction, inexpensive inmanufacture and thoroughly reliable and efficient in operation. Anotherobject is to provide a device of the above nature which is sturdy andwell able to withstand continued, rigorous use. Another object is toprovide a device of the above nature by which the sound volume in aradio or the like may be eifectively controlled without the productionof static. Another object is to provide a device of the above nature,the several parts of which are standardized and which, accordingly,permits high. production requirements to be met readily. Another objectis to provide a device of the above nature readily adaptable forinstallation in commercial radio sets and easily connectable in. circuittherein as desired. Other objects will be in part apparent and in partpointed out.

Ihe invention accordingly consists in the fea tures oi construction,combinations of elements, and arrangements of parts as will beexemplified in the structure to be hereinafter described and the scopeoithe application of which will be indicated in the following claims.

In the accompanying drawings in which is shown one of the variouspossible embodiments of this invention,

Figure l is a rear elevation of the rheostat;

Figure 2 is a rear-elevation oi the .rheostat with certain partstherein? removed;

Figure 3 is a perspective oi the rheostat, certain parts thereof beingremoved;

Figure 4 is an elevationof the resistance strip of the rheostat;

tactor oi the rheostat taken on the line S--fi of.

Fi re 1;

well to point out first that many variable resistance devices of thischaracter are productive of undesirable noises or static duringoperation. Much of this noise can be ascribed to the imperfectengagement between the sliding contact and the resistance strip. Stillanother source of static noise results where resistance strips ofsubstantial width are employed. Other rheostats are unduly complicatedand accordingly expensive due to the manner in which taps are broughtout in them. Such taps must be located with respect to the resistancestrip in accordance with the requirements of purchasers of the rheostat.In many instances it becomes necessary to make special dies for stampingout various parts of the rheostat, thus precluding standardization ofparts. In still other rheostats, particularly in high range volumecontrols, it is dimoult to attain good tone quality, due to leakagecurrent between the parts connected to the sliding contact and the highpotential end of the control. It is ac 4 cordingly another object ofthis invention .to

rectify the above conditions in athoroughly efficie'nt and practicalmanner.

Referring first to Figure 8, my rheostat, gen= erally indicated at it,comprises a base portion ll rotatably Journaling a shaft i2, and coveredby a housing or cover it. Theiront surface of base i i is covered by aplate M (see also Figure 7) this plate being held in place by ears orlugs 13a extending from cover it. As is best shown in Serial No.706,343, filed January 12, 1934.

Figure 7 is a sectional elevation taken on the line iil! of Figure 1;

Figure 8 is a perspective view of the rheostat with a snap switchmounted thereon; and,

Figure 9 is a front elevation of the rheostat.

Base II is preierablymolded from a suitable dielectric such as phenoliccondensation prodnot, and has formed in the front surface thereof (seeFigures 5, if and 9) radially extending recesses It, ll, i8, i9 andflit-(Figure 9) which will be more fully described below. Extending fromthe front surface of base H, I also provide a locating lug or projection2|, which extends through a slot i i-a (Figure 8) in cover plate Hi toproperly locate the cover. A central hole 22 (Figure 9) is formed inbase H, which, as shown in Figure l, receives'a fitting or hearinggenerally indicated at 23. The forward end 230 of bearing 23 ispreferably threaded to provide a suitable mounting for the rheostat inthe panel of a radio set or the like. A collar portion 23b is providedon bearing 23, this collar portion being forced into central hole 22 ofbase ii. The upper portion 23c of bearing 23 is preferably reduced indiameter for a purpose described hereinaiter. Thus, bearing 23 providesa suitable journal for shaft l2, shaft i2 being provided with an annularslot l2a (Figure 7) which receives a spring washer 24 to prevent axialmovement of shaft l2 in bearing 23.

Referring to Figures 2 and 3, it may be seen that the inner surface ofbase Ii is provided with an annular ridge 15 (see also Figures and '4),base Ii also being provided with shoulder portions 30 and 3| (Figures 2and 3), respectively adjacent leads 25, 28 and leads 21, 2B, 29. Asismore clearly shown in Figure 5, shoulders 30 and Ii provide a suitablesupport on base ii for cover l8, whose lugs I30. extend downwardly alongthe sides of base ii between shoulders 30 and II.

The portion of base i i immediately surrounded by ridge (Figure 5) ispreferably recessed as at 32, this recess being provided with an insideborder or ridge 33 extending inwardly from base I I. As is more clearlyshown in Figure '7, a wall 44 projects inwardly from a portion of ridge32, this wall including straight portions 340. and 342: (Figure 2),forming a channel 340 therebetween on the inside surface of base i lthis channel being for a purpose disclosed hereinafter. A

hole in base II and channel 340 between walls 340 and 34b receives arivet 31 (Figure 9) whose outer head retains lead 28 in recess IS. Theinner end lla (Figure 2) of rivet 31 forms an elongated lug orprojection (Figure 3) which acts both to retain one end of a shieldingstrip 38 in operative position in channel 340 and to provide astop for arotatable contact arm 39 (Figure 1), all as will be described in greaterdetail hereinafter. Formed adjacent straight portion 34b of wall 34 anddepressed from the level of base receas I2, I provide a depression 35(Figure 5) this depression preferably being substantially circular inform and sufliciently deep to receive the head of a rivet 3B, the otherhead of which fastens lead 21 in recess i8.

Base ii is also provided with additional holes opening into recesses i6,i1, and (Figure 9) which respectively receive rivets 40, 4i and 42,

the outer ends of which retain respectively leads 2|, 2! and 2! in theirrespective recesses. The inner heads oi! rivets 40, 4| and 42 (Figure 2)retain, within body recess 32, a resistance strip 4! (Figure 5), thisstrip being accordingly provided with holes 43a, 43b and 43c (see Figure4).

Resistance strip 43 (Figure 4) is preferably formed in the general shapeof a horseshoe or annular strip having narrow annular portions 44 and 45and secant portions 46 and 41. Annular portions 44 and 45 arerespectively provided with enlarged portions 48 and 49, these portionshaving highly conductive coatings 48a. and 49a forming a part of theterminal structure, as will be pointed out later. Accordingly, holes42a, 42b and 430 extend through secant portions 44 and 41 and terminalportions 49 respectively. Preierably strip 43 is stamped out of anysuitable ilbrous dielectric material such as canvas impregnated withphenolic condensation product, which has previously been coated with aresistance ink of suitable conductivity. The resistance ink is thenremoved from secant portions 44 and 41 to leave a continuous circularpath 80 of resistance coating or equal width throughout thecircumferential length of the strip. Resistance path 80 is bordered bythe non-conductive surface of the secant portions 46 and 41.Furthermore, no additional material is wasted in providing secantportions 46 and 41 for in stamping out the usual circular strip thecentral portion is pure waste.

Preferably the width of resistance path does not exceed one-eighth of aninch. The advantage inusing such a narrow resistance strip resides inthe reduction of the noise level of the volume control during itsoperation because it is possible to use higher conductivity inks on thenarrow strip. Resistance value depends upon the width of the conductingpath as well as the length thereof. The narrower the width of the path,the less conductivity and the greater the resistance for a given length.Thus the nor row path allows the use of a coating of greaterconductivity for a given resistance value. As noise due to contact ofslider on the resistance element varies inversely with the conductivityof the resistance ink, a quieter operation is assured by providing thenarrow resistance path and high conductivity resistance inlr.

It should be pOi'iittfid out at this time that by forming base Ii(Figure 3), cover plate i4, housing i3 and resistance strip 43, asdescribed hereinabove, all of these parts may be standardized andsubsequently adapted to the requirements oi. diiferent purchasers. Inthis connection. it should first be pointed out that, various purchasersof volume controls require taps to be brought out at various positionsabout resistance strip 43, these taps being connected to leads 25 and26. It is obvious that the requirements of different purchasers willvary, that is, one set oi requirements may require taps to be broughtout in the 12 o'clock and 2 o'clock positions on strip 43 as indicatedby taps ill and Bi (Figure 4). Other requirements may necessitatebringing the taps out at 11 ocloclr and 1 o'clock positions. To meetsuch varying requirements, many manufacturers of volume controls resortto resistance strips stamped with projecting lugs for example, atexactly the positions at which tops are required to be taken oil. Toaccommodate such lugs it is necessary for such manufacturers to formregistering recesses or the like in the support and in the casing orhousing. Thus a number of the parts of the control must be varied tosuit the individual requirements of each purchaser, necessitatingchanges in tools and considerable additional expense.

These difliculties and their attendant waste are overcome in the presentconstruction by standardization of all of the parts of my control. Thus,as pointed out above, tap leads 25 and 26 are always in a predeterminedlocation registering with holes 43a and 4822 (Figure 4) of thestandardized resistance strip 43. Nevertheless, I may tap resistancepath 80 at any point throughout a large portion of its length. For

' example, highly conductive coatings or taps 50 and ii are painted onpath 80 at the required,

points, Portions We and Ila thereof extending over the insulatedsurlaces or secants 45 and 41 to points adjacent holes 43a and 43b. TapsIn and II extend radially across resistance path Ill and terminatebeneath the heads of rivets 40 and 4| (Figures 2, 5 and 7). Rivets 40and 4| extend through base Ii to hold tap leads 25 and-26 in position.Accordingly, tap leads 25 and 2 may be connected to diflerent pointsalong resistance path 80 without changes in tools and with no waste ofmaterials. For a better understanding of the difllculties overcome bythe above-noted standardization, reference ismade to my copendingapplication Serial No. 706,343,

filed January 12,1934.

Contact arm 39 (Figure 1) is preferably stamped from suitable dielectricfibrous material,

and is secured to the top of shaft it (Figure 5) by a rivet 52, thuscoacting with spring washer 2|. to hold shaft l2 in place. The headedportion of rivet 52 rests on the top of a clip 53 provided with anupstanding arm M suitably posi- :8, clip 53 and its arm 5 operate snapswitch l5.

Referring to Figure 1, contact arm 39 has a radially projecting portion58 provided with a hole or slot 51, through which extends o'ne'end 8811(Figure 7) of a retaining strap 59. The other end 591) of strap 59 ispreferably bowed to receive thereunder a suitable number of contactwires 6| (preferably 5); wires 85 are preferably phosphor bronze andround in cross section. As best shown in, Figure 1, portion 66 of arm 39is provided with a pair of slots 56:; and 56b, and

wires 6| which are held under end portion 59b by solder or the like,extend down through slot 552), thence substantially horizontally to formarcuate portions 6la (Figure 6) and thence upwardly through slot 56a toterminate in hook portions Gib. The arcuate portions Bla of wires 5|comprise the contacting portions thereof, and I have found it highlydesirable to use wire for this purpose because of its smooth surface. I

ture described, it is possible to provide a contact of adequatecontacting area, but oi. relatively narrow overall width, well adaptedto cooperate with the narrow resistance path described hereinabove.

To connect contact wires (it (Figure '7) to terminal 21, I provide acoil spring wire 58 wound about an insulating bushing 90 mounted on baseI l. The lower coil of spring 58 rests on shoulder 90a of bushing 91]while the upper coil of the spring bears against contact arm 39. One end58a of the spring is bent into depression 35 and is fastened thereinunder the head of rivet 36, spring end 58a thus being electricallyconnected to terminal 21. Preferably I interpose a, piece SI ofinsulating material between resistance strip 43 and the head of rivet 36to insulate the strip from spring end'58a. The other end 5% of thespring is trained upwardly through contact arm slot 51 and thence alongthe surface of contact arm 39 under strap 59 to which the spring end iselectrically connected, preferably by encircling atlases .10 tioned toengage an actuating arm 55 of snap switch l5. Thus, upon rotation ofcontact arm.

'thus provide an unusually smooth surface to conthe ground potentialthereof. Thus end 49 of resistance strip 43, hereinafter referred to asthe high potential end, can be connected to the high potential side ofthe circuit and end 8 thereof, hereinabove referred to as the lowpotential end can be connected tothe low potential side of the circuit.Accordingly, resistance strip end 9 is hereinafter called the highpotential end, and end 48 thereof is called the low potential endi I Thehigh potential end 49 of resistance strip 43 (Figure 2) is secured onbase H by rivet 36 which connects this end of the strip to lead 21.

Thus the head 36a of rivet 36 contacts highly conductive coating 49a tomake a good electrical connection therewith. Thus the total resistanceto a current flowing from high potential lead 21 to the slider lead 29is determined according to the position of contact wires 6! along theirannular path of travel on resistance path 85; current flows by way oflead 21, resistance strip 43, contact wires 6|, contact strip projection59 and coil spring 58 to lead 29. It will now be clear that tap 28, theground or low potential tap, is located between high potential tap 21and slider tap 29. Thus taps 21 and 29 are not only spaced a substantialdistance from each other but are effectively shielded from each other.

Low potential or ground lead 28 is preferably positioned between highpotential lead 21 and slider lead 29, as best shown in Figure 9. As

described above, ground lead 28 is held in its recess i9 by rivet 31,which secures shield 38 in its position. Shield 38 also includes a portion 38a which depends downwardly (Figures 2 and 5) and contacts highlyconductive end portion 48a, the low potential end of resistance strip43, thus effecting the ground circuit. The other end 38d of shield 38extends into a depression 63 in base H where it is suitably anchored.Intermediate ends 38a and 38d of shield 38 are arcuate shaped portion38b and raised portion 38c extending over head 36a of rivet 36. As ismore clearly shown in Figure l, shield 38 is positioned to overlie thehigh potential end 49 of resistance strip 43 to shield-it from rivet 60(Figures 1 and 7) as well as the other parts connected thereto. Thus thearmature of the control is electrostatically shielded from the highpotential end of the volume control, and I I have found that thisresults in better tone quality especially in a high range volume controlof, for example, controls of two megohms capacity or more.

In operation,'the contact arm 39, when in the position shown in Figure1, provides maximum resistance, being at this point at its greatestdistance fromthe high potential end 49 of resistance strip 43.Consequently, as the slider contact 39 is rotated in a counterclockwisedirection, as viewed in Figure l, the resistance decreases until theslider has reached its maximum volume position, i. e., when the edge ofarm 39 abuts against stop 3ia. It should also be noted that when in thisposition shield 38 effectively shields the high potential terminal fromthe slider contact.

' Accordingly, I have provided a rheostat or volume control whicheffectively accomplishes the several objects noted hereinabove in athorough= ly eificient and practical manner.

As many possible embodiments may be made of the above invention and asmany changes might be made in the embodiment above set forth, it is tobe understood that all matter hereright angles to the axis of saidshaft, a resistance path comprising an annular carbonaceous coating ofeven width on said flat surface of said base inposition for engagementby said contactor and spaced outwardly from said shaft,

terminal connections at the opposite end portions of said path, a tap onsaid base located between said path and said shaft, and a strip ofhighly conductive material applied to said base and running from saidtap across a predetermined point on said path intermediate said terminalconnections to form a good electrical connection between said point andsaid tap, said tap being insulated from said path except at said pointby way of said last-mentioned connection.

2. In apparatus of the class described, in combination, a base, a shaft,a contactor secured to said shaft, said base having a flat dielectricsurface the plane of which is substantially at right angles to the axisof said shaft, a"resistance path in the form of an annular coating ofeven width on said flat surface of said base in position for engagementby said contactor and spaced outwardly from said shaft, terminalconnections at the opposite end portions of said path, a tap on saidbase located between said path and said shaft, and an electricalconnection comprising a strip-like coating othighly conductive materialon said flat surface of said base and running from said tap across apredetermined point on said resistance path intermediate said terminalconnections to form a good electrical connection between said point andsaid tap, said tap being insulated from said path except at said pointby way of said last-mentioned connection.

3 In apparatus of the class described, in combination, a flat piece ofinsulating material substantially horse-shoe shaped and having a secantportion, an annular coating of resistance material on one-surface 01'said piece having a substantially even width bordered on its inner edgethroughout a portion of its length by said secant portion, an electricalconnector mounted on said secant portion, and a ribbon-like highlyconductive coating extending radially from. said resistance coating andacross said secant portion to said connector.

4. In apparatus of the class described. in combination, a base, aresistance strip mounted on said base, a contact slider mounted forslidlhl contact with said resistance strip, a high potential terminal, alow potential terminal and a slider terminal, all of said terminalsbell)! mounted on said base, said high potential and slider terminalsbeing respectively connected to the high potential end of said strip andsaid slider contact and said low potential terminal being connected withthe low potential end of said strip and disposed between said highpotential terminal and said slider contact, said base beingsubstantially annular in shape and having one portion wider than theremaining portion, and extending inwardly therefrom, said resistancestrip comprising a substantially annular coating of resistance materialof substantially even width and following the outer edge of said base,the enlarged portion of said base adjacent said coating having adielectric surface, a tap mounted on said enlarged portion, and aribbonlike coating of highly conductive material extending across saidresistance coating and across said dielectric surface and engaging saidtap. 5. In apparatus of the class described, in combination, a base, asubstantially circular resistance strip comprising a coating ofcarbonaceous material on said base, a rotatable mounted in said base, acontact support mounted on said shaft and extending radially therefromover said strip, said support having a slot formed therein above saidstrip, and. a ccntactor forv slidably contacting said strip comprising aplurality of spring wires round in cross section, each having an endanchored. to said support and thence extending downwardly and outward-1y from said support in a direction substantially at right angles to theradial center of said support to engage the fiat surface p. 3 saidresistance strip, the free ends of each of ""1 then turning upwardlyaway said strip through said slot in said sup; a smooth rounded portionthereof in gernent with the carbonaceous surface of said strip.

6. In apparatus of the class described, in combination, a flat piece ofinsulating material hailing the general shape of a horseshoe and havin aflat surface, an annular strip oi resistance material on said surface,said piece having a secant portion adjacent the inner r' c of said stripand extending throughout a port-ion of the length of said strip, thesurface of said secant portion being dielectric, an electrical connectormounted on said secant portion, and a highly conductive coatingconnected to a point on. said resistance strip adjacent said secantportion and extending therefrom across said secant portion, said coatingbeing connected to said connector.

JESSE MARS'I'EN.

